A number of fabrication techniques have been used to couple leaflets to the inside of a conduit, including sewing individual leaflets to the inner surface of the conduit. In many cases, the resulting leaflet is supported on the inside surface of the conduit and defines a flap having a mounting edge where the leaflet is coupled to the inside surface of the conduit and a free edge that allows the flap to move. The flap moves under the influence of fluid pressure. In operation, the leaflets open when the upstream fluid pressure exceeds the downstream fluid pressure allowing flow through the conduit and closes when the downstream fluid pressure exceeds the upstream fluid pressure and blocks the flow through the conduit.
The process for mounting the leaflet to the inside surface of the conduit is tedious, time consuming and requires great skill. The conduit is everted to expose the inside surface of the conduit. The leaflet is precisely cut to the correct size and shape. The attachment edge of the leaflet is sewn by hand onto the everted conduit. Additional leaflets, commonly three total, are sewn circumferentially around the everted conduit. Once attached to the inside surface of the conduit, the conduit is reverted with the expectation that the three leaflets are properly placed. The three leaflets must cooperate with each other such that they may coapt at their free edges to create a seal and prevent flow during the closed phase of the cardiac cycle.
Valved conduits made in this way present significant challenges. The leaflets must be precisely cut to size and shape prior to attachment. Placement of the leaflets on the inside surface of the conduit while in an everted state and relative to the other leaflets must be held to high tolerances, usually placed by hand with without alignment tools or jigs. The punctures of the attachment edge with a needle for receiving suture not only have to be precisely placed by hand, but the number of punctures must be limited to reduce structural weakening along the attachment edge. Further, all of the punctures and resulting suture passing therethrough is exposed to the blood flow and are located precisely at the line of flexure of the leaflet at the leaflet base, which can lead to reduced durability.
Leaflet durability under the repetitive loads of the leaflets opening and closing is dependent, in part, on the load distribution between the leaflet and the conduit wall. Further, substantial load is encountered on the leaflet when in the closed position. Mechanical failure of the leaflet can arise, for example, at the mounting edge, where the flexible leaflet is attached by the suture, particularly at the commissure region. The repetitive loads of the leaflet opening and closing leads to material failure by fatigue, creep or other mechanism, depending in part on the leaflet material. Mechanical failure at the mounting edge is especially prevalent with synthetic leaflets.
Therefore, there remains a significant need for a valved conduit, encompassing a conduit and a valve structure, with long durability and easier manufacture.